1. Field of the Invention
The invention relates to method of fabricating a semiconductor laser diode using selective growth.
2. Description of the Related Art
A conventional method of fabricating a semiconductor laser diode using selective growth is disclosed in Japanese patent application laid-open No. 6-260727.
According to the conventional method, strip-shaped masks for selective growth are formed on a semiconductor substrate. Then, using metal organic chemical vapor deposition (MOCVD), a lower clad layer, a multiple quantum well (MQW) active layer and an upper clad layer are formed between the selective growth masks in the stated order. With this method, not using etching, a ridge waveguide structure is fabricated.
However, according to the conventional method of fabricating a semiconductor laser diode, in a step for removing the selective growth mask, side walls of the ridge structure are exposed to the air. Although a top surface of the MQW active layer is covered with the upper clad layer, side portions of the active layer are exposed. Therefore, surface state is generated in the MQW active layer so that property of the semiconductor laser diode becomes worse.
It is therefore an object of the invention to provide a method of fabricating a semiconductor laser diode, counters against the above-described problem.
According to the present invention, such a method includes forming a mask layer on a semiconductor substrate and forming a ridge waveguide structure including an active layer on the semiconductor substrate by selective growth method using the mask layer. The mask layer is formed to be along a direction with an angle to [011] direction of the semiconductor substrate
Side portions of the active layer are mostly covered with the upper grown layer so that portions of the active layer exposing to the air are relatively small. Therefore, comparing to the conventional method, it is possible to reduce the surface state of the active layer.